Method and instruments for non-invasive analyte measurement

ABSTRACT

The present invention is related to optical non-invasive methods and instruments to detect the level of analyte concentrations in the tissue of a subject. The spectra of mid-infrared radiation emitted from a subject&#39;s body are altered corresponding to the concentration of various compounds within the radiating tissue. In one aspect of the invention, an instrument measures the level of mid-infrared radiation from the subject&#39;s body surface, such as the eye, and determines a specific analyte&#39;s concentration based on said analyte&#39;s distinctive mid-infrared radiation signature.

CROSS-REFERENCE TO RELATED APPLICATION

Applicants claim the benefit of prior provisional application60/467,355, filed on May 2, 2003 under 35 U.S.C. 119(e).

FIELD OF THE INVENTION

The present invention is related to optical non-invasive methods andinstruments to detect the presence or measure the concentration of awide range of analytes, such as glucose, in the tissue of a subject. Thespectra of mid-infrared radiation emitted from the subject's body arealtered corresponding to the presence, absence or concentration of theanalyte within the subject's tissue. In one aspect of the invention, aninstrument measures the level of mid-infrared radiation from a surfaceof the subject's body, including but not limited to mid-infraredradiation emitted from any body surface, such as the skin or the eye,any orifice, piercing tract, or cavity, such as the mouth, ear or nose,and determines a specific analyte's presence or concentration based onsaid analyte's distinctive mid-infrared radiation signature. Themeasurements made by the instrument of the present invention do notrequire direct contact of the instrument with a surface of a subject'sbody.

BACKGROUND OF THE INVENTION

Diabetes remains one of the most serious and under-treated diseasesfacing the worldwide healthcare system. Diabetes is a chronic diseasewhere the body fails to maintain normal levels of glucose in thebloodstream. It is now the fifth leading cause of death from disease inthe U.S. today and accounts for about 15% of the entire healthcarebudget. People with diabetes are classified into two groups: Type 1(formerly known as “juvenile onset” or “insulin dependent” diabetes,that are required to take insulin to maintain life) and Type 2 (formerlyknown as “adult onset” or “non-insulin dependent,” that may requireinsulin but may sometimes be treated by diet and oral hypoglycemicdrugs). In both cases, without dedicated and regular blood glucosemeasurement, all patients face the possibility of the complications ofdiabetes that include cardiovascular disease, kidney failure, blindness,amputation of limbs and premature death.

The number of cases of diabetes in the U.S. has jumped 40% in the lastdecade. This high rate of growth is believed to be due to a combinationof genetic and lifestyle origins that appear to be a long-term trend,including obesity and poor diet. The American Diabetes Association (ADA)and others estimate that about 17 million Americans and over 150 millionpeople worldwide have diabetes, and it is estimated that up to 40% ofthese people are currently undiagnosed. American Diabetes Association,“Facts & Figures.”

Diabetes must be “controlled” in order to delay the onset of the diseasecomplications. Therefore, it is essential for people with diabetes tomeasure their blood glucose levels several times per day in an attemptto keep their glucose levels within the normal range (80 to 130 mg/dL).These glucose measurements are used to determine the amount of insulinor alternative treatments necessary to bring the glucose level to withintarget limits. Self-Monitoring of Blood Glucose (SMBG) is an ongoingprocess repeated multiple times per day for the rest of the patient'slifetime.

All currently FDA approved invasive or “less-invasive” (blood taken fromthe arm or other non-fingertip site) glucose monitoring productscurrently on the market require the drawing of blood in order to make aquantitative measurement of blood glucose. The ongoing and frequentmeasurement requirements (1 to possibly 10 times per day) presents alldiabetic patients with pain, skin trauma, inconvenience, and infectionrisk resulting in a general reluctance to frequently perform thecritical measurements necessary for selecting the appropriate insulindose or other therapy.

These current product drawbacks have led to a poor rate of patientcompliance. Among Type 1 diabetics, 39% measure their glucose levelsless than once per day and 21% do not monitor their glucose at all.Among Type 2 diabetics who take insulin, only 26% monitor at least onceper day and 47% do not monitor at all. Over 75% of non-insulin-takingType 2 diabetics never monitor their glucose levels. Roper StarchWorldwide Survey. Of 1,186 diabetics surveyed, 91% showed interest in anon-invasive glucose monitor. [www.childrenwithdiabetes.com] As such,there is both a tremendous interest and clinical need for a non-invasiveglucose sensor.

The present invention seeks to replace the currently used blood glucosemeasurement methods, devices and instruments, including invasivemeasures and the use of glucose test strips, with an opticalnon-invasive instrument.

Various methods have been developed related to non-invasive glucosesensing using a dermal testing site such as the finger or earlobe. Thesemethods primarily employ instruments which measure blood-glucoseconcentration by generating and measuring light only in thenear-infrared radiation spectrum. For example, U.S. Pat. No. 4,882,492(the '492 patent), expressly incorporated by reference herein, isdirected to an instrument which transmits near-infrared radiationthrough a sample to be tested on the skin surface of a human. In the'492 patent, the near-infrared radiation that passes through the sampleis split into two beams, wherein one beam is directed through a negativecorrelation filter and the second through a neutral density filter. Thedifferential light intensity measured through the filters of the twolight beams is proportional to glucose concentration according to the'492 patent.

U.S. Pat. No. 5,086,229 (the '229 patent), expressly incorporated byreference herein, is directed to an instrument which generatesnear-infrared radiation within the spectrum of about 600 to about 1100nanometers. According to the '229 patent, a person places their fingerin between the generated near-infrared radiation source and a detector,which correlates the blood-glucose concentration based on the detectednear-infrared radiation. Similarly, U.S. Pat. No. 5,321,265 (the '265patent), expressly incorporated by reference herein, also measuresblood-glucose level using both near-infrared radiation and the fingertipas a testing site. The detectors disclosed in the '265 patent furthercomprise silicon photocells and broad bandpass filters.

U.S. Pat. No. 5,361,758 (the '758 patent), expressly incorporated byreference herein, is directed to an instrument which measuresnear-infrared radiation that is either transmitted through or isreflected from the finger or earlobe of a human. In the '758 patent, thetransmitted or reflected light is separated by a grating or prism, andthe near-infrared radiation is detected and correlated withblood-glucose concentration. This instrument of the '758 patent alsocomprises an additional timing and control program wherein the devicetakes measurements specifically in between heartbeats and can alsoadjust for temperature.

U.S. Pat. No. 5,910,109 (the '109 patent), expressly incorporated byreference herein, is also directed to an instrument for measuringblood-glucose concentration using near-infrared radiation and theearlobe as the testing site. The instrument of the '109 patent comprisesfour light sources of a very specific near-infrared emission spectrum,and four detectors having specific near-infrared detection spectracorresponding to the wavelength of the light sources. The signalsdetected by the four distinct detectors are averaged, and these averagesare analyzed to determine blood-glucose concentration according to the'109 patent.

The technique of using near-infrared radiation, wherein thenear-infrared radiation is transmitted through or reflected from adermal testing site and monitored for measuring glucose in vivo, isknown to be inaccurate. The glucose concentration of interest is in theblood or the interstitial fluid, not on the surface of the dermis.Therefore these methods must penetrate down into the layers beneath thetop layers of dermis. There are a number of substances in the dermisthat can interfere with the near-infrared glucose signal. Additionally,there is a wide variation in the human dermis, both between individualsand within a given individual. Moreover, glucose simply lacks asatisfactory distinguishable “fingerprint” in the near-infraredradiation spectrum. Because near-infrared radiation is not sufficientlyadsorbed by glucose and because of the level of tissue interferencesfound in the dermis, this technique is substantially less desirable forthe accurate measurement of blood-glucose concentrations.

U.S. Pat. No. 6,362,144 (the '144 patent), expressly incorporated byreference herein, discloses using the fingertip as a testing site,however, the described instrument uses attenuated total reflection (ATR)infrared spectroscopy. According to the '144 patent, a selected skinsurface, preferably the finger, is contacted with an ATR plate whileideally maintaining the pressure of contact. In the '144 patent, theskin is then irradiated with a mid-infrared beam, wherein said infraredradiation is detected and quantified to measure blood-glucose levels.This technique is not ideal, however, if the surface of tissue fromwhich the measurement is taken is very dense in the wavelength region ofinterest or is not amenable to direct contact with the ATR plate, suchas an eye, nose, mouth, or other orifice, cavity or piercing tract.

The minimal depth of peripheral capillaries in epithelial tissues istypically about 40 microns. Again, there are physical characteristics aswell as a number of substances present in the skin that can interferewith the desired glucose-specific signal. While useful in thelaboratory, both the near-infrared transmission methods, and the ATRmethod mentioned above are not practical, or may not be adequate for usein monitoring blood glucose concentration in patients.

Methods have also been developed related to non-invasive glucose sensingusing the eye as a testing site. For example, in both U.S. Pat. Nos.3,958,560 (the '560 patent) and 4,014,321 (the '321 patent), bothexpressly incorporated by reference herein, a device utilizing theoptical rotation of polarized light is described. In the '560 and the'321 patents, the light source and light detector are incorporated intoa contact lens which is placed on the surface of the eye whereby the eyeis scanned using a dual source of polarized radiation, each sourcetransmitting in a different absorption spectrum at one side of thecornea or aqueous humor. The optical rotation of the radiation thatpasses through the cornea correlates with the glucose concentration inthe cornea according to the '560 and '321 patents. While this methodwould be termed, “non-invasive,” because the withdrawal of blood is notrequired, it may still cause significant discomfort or distort vision ofthe user because of the need to place the sensor directly on the eye.

U.S. Pat. No. 5,009,230 (the '230 patent), expressly incorporated byreference herein, uses a polarized light beam of near-infrared radiationwithin the range of 940 to 1000 nm. In the '230 patent, the amount ofrotation imparted by glucose present in the bloodstream of the eye onthe polarized light beam is measured to determine glucose concentration.Again, the accuracy is limited because glucose simply lacks asufficiently distinguishable “fingerprint” in this near-infraredradiation spectrum.

Both U.S. Pat. No. 5,209,231 (the '231 patent), and InternationalPublication No. WO 92/07511 (the '511 application), both expresslyincorporated by reference herein, similarly disclose the use ofpolarized light, which is initially split by a beam splitter into areference beam and a detector beam, and then transmitted through aspecimen, preferably the aqueous humor of the eye. The amount of phaseshift as compared between the transmitted reference and detector beamsare correlated to determine glucose concentration in the '231 patent and'511 application. U.S. Pat. No. 5,535,743 (the '743 patent), expresslyincorporated by reference herein, measures diffusely reflected lightprovided by the surface of the iris as opposed to the aqueous humor ofthe eye. According to the '743 patent, the measurement of opticalabsorption is possible whereas measurement of the optical rotationthrough the aqueous humor is not possible. In the '743 patent, theintensity of the diffusely reflected light, however, may be analyzed toobtain useful information on the optical properties of the aqueoushumor, including blood-glucose concentration.

U.S. Pat. No. 5,687,721 (the '721 patent), expressly incorporated byreference herein, also discloses a method of measuring blood-glucoseconcentration by generating both a measurement and reference polarizedlight beam, and comparing said beams to determine the angle of rotation,which is attributable to the blood-glucose concentration. The preferabletesting site disclosed, however, is the finger or other suitableappendage according to the '721 patent. The '721 patent furtherdiscloses and requires the use of a monochromatic laser and/orsemi-conductor as a light source.

U.S. Pat. No. 5,788,632 (the '632 patent), expressly incorporated byreference herein, discloses a non-invasive instrument for determiningblood-glucose concentration by transmitting a first beam of lightthrough a first polarizer and a first retarder, then directing the lightthrough the sample to be measured, transmitting the light through asecond polarizer or retarder, and lastly detecting the light from thesecond detector. The rotation of measured polarized light is correlatedto the blood-glucose concentration of the sample measured according tothe '632 patent.

U.S. Pat. No. 5,433,197 (the '197 patent), expressly incorporated byreference herein, discloses a non-invasive instrument for determiningblood-glucose concentration using a broad-band of near-infraredradiation which illuminates the eye in such a manner that the energypasses through the aqueous humor in the anterior chamber of the eye andis then reflected from the iris. The reflected energy then passes backthrough the aqueous humor and the cornea and is collected for spectralanalysis. According to the '197 patent, the electrical signalsrepresentative of the reflected energy are analyzed by univariate and/ormultivariate signal processing techniques to correct for any errors inthe glucose determination. Again, the accuracy of the instrument in the'197 patent is limited because glucose simply lacks a sufficientlydistinguishable “fingerprint” in this near-infrared radiation spectrum.

Instruments and methods of using the body's naturally emitted radiationto measure blood-glucose concentration using the human-body, and inparticular, the tympanic membrane as a testing site have also beendisclosed. U.S. Pat. Nos. 4,790,324; 4,797,840; 4,932,789; 5,024,533;5,167,235; 5,169,235; and 5,178,464, expressly incorporated by referenceherein, describe various designs, stabilization techniques andcalibration techniques for tympanic non-contact thermometers. Inaddition, U.S. Pat. No. 5,666,956 (the '956 patent), expresslyincorporated by reference herein, discloses an instrument which measureselectromagnetic radiation from the tympanic membrane and computesmonochromatic emissivity using Plank's law by measuring the radiationintensity, spectral distribution, and blackbody temperature. Accordingto the '956 patent, the resultant monochromatic emissivity is variabledepending on the spectral characteristics of the site measured, namelythe blood-glucose concentration measured from the tympanic membrane. Itshould be noted, however, that the '956 patent equates skin surfaces ofthe body to a “gray-body” rather than a black-body with respect to itsmonochromatic emissivity. Therefore, according to the '956 patent, theaccuracy of such skin surface-based methods utilizing natural black-bodyemitted radiation is not useful for analyte measurements, as compared toa method of subsurface analysis utilizing natural black-body radiationemitted from the tympanic membrane.

The human body naturally emits from its surfaces infrared radiationwhose spectrum, or radiation signature, is modified by the presence,absence or concentration of analytes in the body tissues. The eye isparticularly well suited as a testing site to detect this infraredradiation. For example, certain analytes, such as glucose, exhibit aminimal time delay in glucose concentration changes between the eye andthe blood, and the eye provides a body surface with few interferences.Cameron et al., (3)2 DIABETES TECHNOL. THER., 202–207 (2001). There is,therefore, in the field of non-invasive blood analyte monitoring, anunmet need for a suitable instrument, and methodologies for using it, toaccurately measure analyte concentrations, such as blood glucoseconcentration, as well as concentrations of other desired analytes, insubjects requiring this type of blood analyte measurement.

SUMMARY OF THE INVENTION

The present invention is related to non-invasive methods for measuringthe presence or the concentration of a blood or tissue analyte, andinstruments for making such measurements, utilizing the radiationsignature of the natural black-body radiation emission from a subject'sbody surface. The instruments and methods of the present invention donot require direct contact of the instrument with a surface of asubject's body in order to make the analyte measurements.

The analyte that is actually measured or detected may be any compound orsubstance that has a radiation signature in the mid-infrared range. Inaddition to directly measuring the presence, absence or concentration ofa particular analyte, the methods and instrument of the presentinvention may also be used to detect the presence, absence orconcentration of any compound or substance that represents a surrogatemarker for or has a correlation to the presence, absence, orconcentration of another analyte of interest, including but not limitedto any metabolite or degradation product of an analyte, or an upstreamor downstream pathway component or product that is affected by ananalyte of interest. In this situation the analyte that is actuallymeasured is a surrogate marker for another analyte of interest.

One embodiment of the present invention relates to a method of measuringan analyte concentration in the blood or tissue of a subject which maycomprise detecting the level of mid-infrared radiation naturally emittedfrom a body surface of the subject, and determining the analyteconcentration by correlating the spectral characteristics of themid-infrared radiation to the analyte concentration, and analyzing thisdetected mid-infrared radiation to calculate the analyte concentration.In this embodiment, the detecting and correlating steps may furthercomprise using a microprocessor. The subject being tested may be anymammal or non-mammalian animal, and preferably the subject may be ahuman. Further, the analyte being measured may be a wide variety ofanalytes, including, but not limited to, analytes found in the blood orother tissues of a subject, airborne analytes such as those present inair that was contacted with or exhaled by a subject, metabolic compoundsor substances, carbohydrates such as sugars including glucose, proteins,peptides, or amino acids, fats or fatty acids, triglycerides,polysaccharides, alcohols including ethanol, pharmaceutical ornon-pharmaceutical compounds, substances, or drugs. In one embodiment,the analyte being measured is glucose. In addition, the body surfacefrom which the radiation signature is obtained to determine thepresence, absence or concentration of an analyte may be a wide varietyof body surfaces, including, but not limited to, skin, the eye, mouth,nose, ear or any other orifices, cavities, piercing tracts or othersurface of a subject's body whether naturally occurring or artificialsuch as a surgically created body surface.

In another embodiment, the present invention relates to an instrumentwhich measures the level of mid-infrared radiation from a surface of asubject's body and determines a specific analyte's concentration basedon the analyte's distinctive mid-infrared radiation signature. Inanother embodiment, the instrument may also comprise a microprocessorand a display. In another embodiment, the instrument may also comprise awavelength selector which may further comprise a filter of any suitabletype, including but not limited to, an absorption filter, interferencefilter, monochromator, linear variable filter, circular variable filter,and a prism. In another embodiment, the instrument may also comprise amid-infrared light detector, which may be any suitable type, including,but not limited to a thermocouple, a thermistor, a microbolometer, and aliquid nitrogen cooled MTC.

In another embodiment of the present invention, the instrument maycomprise a display, such as an alphanumeric display, including, but notlimited to, a liquid crystal display (LCD), a plasma display panel(PDP), and a field emission display (FED). In another embodiment of thepresent invention, the instrument comprises an audio display which maybe provided with an audio source comprising recorded audio clips, speechsynthesizers and voice emulation algorithms to audibly report theanalyte concentration.

In another embodiment, the instrument of the present invention comprisesa microprocessor and a memory which is operatively linked to themicroprocessor. The instrument of this embodiment may also furthercomprise a communications interface adapted to transmit data from theinstrument to a computer system. In this embodiment, the communicationsinterface selected may be any suitable interface, including, but notlimited to, a serial, parallel, universal serial bus (USB), FireWire,Ethernet, fiber optic, co-axial, and twisted pair cables.

In another embodiment, the present invention relates to a computersystem for downloading and storing measured analyte concentrations. Thisembodiment may further comprise a computer processor, a memory which isoperatively linked to the computer processor, a communications interfaceadapted to receive and send data within the computer processor, and acomputer program stored in the memory which executes in the computerprocessor. The computer processor of this embodiment further comprises adatabase, wherein data received by the processor may be stored on thememory as a database, and sorted into predetermined fields, and thedatabase may be capable of graphical representations of the downloadedanalyte concentrations. The graphical representations of this embodimentmay include, but are not limited to, column, line, bar, pie, XY scatter,area, radar, and surface representations.

In another embodiment, the present invention relates to a computerinterface which is further adapted to transmit data for analyteconcentrations to a remote computer processor or user. In thisembodiment, a remote user may be physicians, research institutes,specialists, nurses, hospice service providers, insurance carriers, andhealth care providers.

In a further embodiment, the present invention relates to a method orsystem for downloading and storing a subject's analyte concentrationswhich may comprise measuring the analyte concentration using anon-invasive instrument having a communications interface, connectingthe non-invasive instrument through the communications interface to acomputer system having a computer processor, a computer program whichexecutes in the computer processor, and an analogous communicationsinterface, and downloading the measured analyte concentrations from thenon-invasive instrument to the computer system. The communicationsinterface of this embodiment further comprises a communicationsinterface adapted to transmit data from the instrument to a computersystem. In this embodiment, the communications interface may include,for example, serial, parallel, universal serial bus (USB), FireWire,Ethernet, fiber optic, co-axial, and twisted pair cables.

Other objectives, features and advantages of the present invention willbecome apparent from the following detailed description. The detaileddescription and the specific examples, although indicating specificembodiments of the invention, are provided by way of illustration only.Accordingly, the present invention also includes those various changesand modifications within the spirit and scope of the invention that maybecome apparent to those skilled in the art from this detaileddescription.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1: Provides a graphical illustration of the human eye.

FIG. 2: Provides a chart that depicts the mid-infrared radiationspectral fingerprint for glucose.

FIG. 3: Provides a graphical illustration of one embodiment of thepresent invention, wherein analyte concentration is measured from themid-infrared radiation reflected back from the eye.

FIG. 4: Provides a flowchart of one embodiment of the present invention,comprising a method wherein a remote access user can receive a subject'smeasured analyte concentrations which have been downloaded and stored ina computer system.

DETAILED DESCRIPTION OF THE INVENTION

It is understood that the present invention is not limited to theparticular methodologies, protocols, instruments, and systems, etc.,described herein, as these may vary. It is also to be understood thatthe terminology used herein is used for the purpose of describingparticular embodiments only, and is not intended to limit the scope ofthe present invention. It must be noted that as used herein and in theappended claims, the singular forms “a,” “an,” and “the” include pluralreference unless the context clearly dictates otherwise. Thus, forexample, a reference to “a mid-infrared filter” is a reference to one ormore filters and includes equivalents thereof known to those skilled inthe art, and so forth.

Unless defined otherwise, all technical and scientific terms used hereinhave the same meanings as commonly understood by one of ordinary skillin the art to which this invention belongs. Preferred methods, devices,and materials are described, although any methods and materials similaror equivalent to those described herein can be used in the practice ortesting of the present invention. All references cited herein areincorporated by reference herein in their entirety.

DEFINITIONS

-   -   Analyte: As used herein describes any particular substance to be        measured. Analyte may also include any substance in the tissue        of a subject, or is present in air that was in contact with or        exhaled by a subject, which demonstrates and infrared radiation        signature. Examples of analytes include, but are not limited to,        metabolic compounds or substances, carbohydrates such as sugars        including glucose, proteins, peptides, or amino acids, fats or        fatty acids, triglycerides, polysaccharides, alcohols including        ethanol, toxins, hormones, vitamins, bacteria-related        substances, fungus-related substances, virus-related substances,        parasite-related substances, pharmaceutical or        non-pharmaceutical compounds, substances, pro-drugs or drugs,        and any precursor, metabolite, degradation product or surrogate        marker of any of the foregoing. Analyte may also include any        substance which is foreign to or not normally present in the        body of the subject.    -   Far-Infrared Radiation: As used herein refers to any radiation,        either generated from any source or naturally emitted, having        wavelengths of about 50.00 to about 1000.00 microns.    -   Focused: As used herein means mostly parallel rays of light that        are caused to converge on a specific predetermined point.    -   Infrared Radiation: As used herein refers to any radiation,        either generated from any source or naturally emitted, having        wavelengths of about 0.78 to about 1000.00 microns.    -   Mid-Infrared Radiation: As used herein refers to any radiation,        either generated from any source or naturally emitted, having        wavelengths of about 2.50 microns to about 50.00 microns.    -   Mid-Infrared Radiation Detector: As used herein refers to any        detector or sensor capable of registering infrared radiation.        Examples of a suitable infrared radiation detectors, include but        are not limited to, a thermocouple, a thermistor, a        microbolometer, and a liquid nitrogen cooled MTC. The combined        detected infrared radiation may be correlated with wavelengths        corresponding to analyte concentrations using means such as the        Fourier transform to produce high resolution spectra.    -   Near-Infrared Radiation: As used herein refers to any radiation,        either generated or naturally emitted, having wavelengths of        about 0.78 to about 2.50 microns.    -   Surface: As used herein refers to any part of a subject's body        that may be exposed to the external environment, including but        not limited to, skin, the eye, ear, mouth, nose or any other        orifice, body cavities, piercing tracts or other surface whether        naturally occurring or artificial such as a surgically created        surface.    -   Tissue: As used herein includes any tissue or component of a        subject, including, but not limited to, skin, blood, body        fluids, the eye, interstitial fluid, ocular fluid, bone, muscle,        epithelium, fat, hair, fascia, organs, cartilage, tendons,        ligaments, and any mucous membrane.        Non-invasive Glucose Measurement

Human beings are natural emitters or radiators of energy in themid-infrared radiation spectrum. In one aspect of the present invention,the body acts as its own light (or heat) source, providing themid-infrared radiation signature of the analytes present therein. Inthis aspect, and with respect to the surfaces of a subject's body, light(or heat) from the body is emitted or radiated from a body surface, andis detected by a mid-infrared detection instrument. The mid-infraredradiation signature in the body's mid-infrared radiation emission isaffected by the presence, absence or concentration of analytes, such asglucose, in the tissues of a subject. The natural mid-infrared radiationsignature of glucose contained within the body's natural mid-infraredradiation signature provides the basis for a non-invasive glucosemeasurement method and instruments for making such measurements (FIG.3). In addition, decreasing or increasing the concentration of certainanalytes may cause an increase in the body's natural emission ofinfrared radiation. Such an increase in the body's natural infraredradiation emission may provide a measurable signal that may be utilizedto measure the presence, absence or concentration of an analyte.

There is substantial evidence that fluctuations in blood glucose levelsare well correlated with glucose levels in the aqueous humor of the eye.(Steffes, 1(2) DIABETES TECHNOL. THER., 129–133 (1999)). In fact, it isestimated that the time delay between the blood and aqueous humorglucose concentration averages only about five minutes. (Cameron et al.,3(2) DIABETES TECHNOL. THER., 201–207 (2001)). The aqueous humor is awatery liquid that lies between the lens and cornea, which bathes andsupplies the nutrients to the cornea, lens and iris (FIG. 1). Theglucose in the eye is located throughout the various components andcompartments of the eye, including, but not limited to, epithelialcells, the aqueous humor, the vitreous humor, various layers of thecornea, iris, various layers of the sclera, conjunctiva, tears, andblood vessels. Therefore, the eye is both an ideal and suitable bodysurface for non-invasive measurement of the presence, absence orconcentration of analytes in the tissue of a subject.

Measuring Mid-infrared Radiation

When electromagnetic radiation is passed through a substance, it caneither be absorbed or transmitted, depending upon its frequency and thestructure of the molecules it encounters. Electromagnetic radiation isenergy and hence when a molecule absorbs radiation it gains energy as itundergoes a quantum transition from one energy state (E_(initial)) toanother (E_(final)). The frequency of the absorbed radiation is relatedto the energy of the transition by Planck's law:E_(final)−E_(initial)=E=hn=hc/l. Thus, if a transition exists which isrelated to the frequency of the incident radiation by Planck's constant,then the radiation can be absorbed. Conversely, if the frequency doesnot satisfy the Planck expression, then the radiation will betransmitted. A plot of the frequency of the incident radiation vs. somemeasure of the percent radiation absorbed by the sample is the radiationsignature of the compound. The absorption of some amount of theradiation that is applied to a substance, or body surface containingsubstances, that absorbs radiation may result in a measurable decreasein the amount of radiation energy that actually passes through, or isaffected by, the radiation absorbing substances. Such a decrease in theamount of radiation that passes through, or is affected by, theradiation absorbing substances may provide a measurable signal that maybe utilized to measure the presence, absence or the concentration of ananalyte.

The human body emits electromagnetic radiation within the infraredradiation spectrum. The spectral characteristics of the infraredradiation emitted can be correlated with the properties of the emittingobject, such as a subject's body surface. For example, glucose absorbsmid-infrared radiation at wavelengths between about 8.0 microns to about11.0 microns. If mid-infrared radiation passes through or reflects froman object where glucose is present, a distinct radiation “fingerprint”or “signature” can be detected from the remaining light that is notabsorbed, creating a radiation signature. The radiation signaturecreated can both confirm the presence or absence of an analyte andindicate the concentration of an analyte. In addition, since glucose isa radiation absorbing substance, there may be a measurable decrease inthe amount of radiation energy that passes through or reflects from aglucose containing material such as the body surfaces of a subject,including the subject's eye. This measurable decrease in the amount ofradiation energy may be utilized to measure the presence, absence orconcentration of glucose in a subject.

One embodiment of the present invention provides a method fornon-invasively measuring the analyte concentration in a tissue of asubject, such as blood, comprising the steps of detecting mid-infraredradiation emitted by the subject, and determining the concentration ofsaid analyte by correlating the spectral characteristics of the detectedmid-infrared radiation with a radiation signature that corresponds tothe analyte concentration, and analyzing the radiation signature to givean accurate analyte concentration measurement. In another embodiment,the method includes a filtering step before detection by filtering thenaturally emitted infrared radiation from the body surface so that onlywavelengths of about 8.00 microns to about 11.00 pass through thefilter. In this embodiment, the filtering step may be accomplished usingabsorption filters, interference filters, monochromators, linear andcircular variable filters, prisms or any other functional equivalentknown in the art. The detecting step may be accomplished using anymid-infrared radiation sensor known in the art, including, but notlimited to a thermocouple, thermistor, microbolometer, a liquid nitrogencooled MTC, or any other functional equivalent known in the art.Correlating the spectral characteristics of the detected mid-infraredradiation may comprise the use of a microprocessor to correlate thedetected mid-infrared radiation signature with a radiation signature ofan analyte. If the analyte being measured is glucose, then the generatedradiation signature may be within the wavelength range within about 8.0to about 11.0 microns. The analyzing step may further comprise amicroprocessor using algorithms based on Plank's law to correlate theradiation signature with glucose concentration.

In another embodiment of the present invention, an instrument comprisinga mid-infrared radiation detector and a display may be held up to a bodysurface of a subject. The naturally emitted infrared radiation from thebody surface may optionally be filtered so that only wavelengths ofabout 8.0 microns to about 11.0 microns reach the mid-infrared radiationdetector, if glucose is the analyte of interest. The radiation signatureof the mid-infrared radiation detected by the detector may then becorrelated with a radiation signature that corresponds to a glucoseconcentration. The radiation signature may then be analyzed to give anaccurate glucose concentration measurement. The measured glucoseconcentration may be displayed.

The instrument of the present invention may also comprise a mid-infraredradiation detector for detecting mid-infrared radiation. Themid-infrared radiation detector can measure the naturally emittedmid-infrared radiation in any form, including in the form of heatenergy. Detecting the naturally emitted mid-infrared radiation may beaccomplished using thermocouples, thermistors, microbolometers, liquidnitrogen cooled MTC, or any other functional equivalent known in theart. Both thermocouples and thermistors are well known in the art andare commercially available. For example, thermocouples are commonly usedtemperature sensors because they are relatively inexpensive,interchangeable, have standard connectors and can measure a wide rangeof temperatures (http://www.picotech.com). In addition, Thermometricsproduct portfolio comprises a wide range of thermistors (thermallysensitive resistors) which have, according to type, a negative (NTC), orpositive (PTC) resistance/temperature coefficient(http://www.thermometrics.com).

The instrument of the present invention may also comprise amicroprocessor. The microprocessor of this embodiment correlates thedetected mid-infrared radiation with a radiation signature whosespectral characteristics provide information to the microprocessor aboutthe analyte concentration being measured. The microprocessor of thisembodiment analyzes the resultant radiation signature using algorithmsbased on Plank's law to translate the radiation signature into anaccurate analyte concentration measurement in the sample being measured.Clinical Applications

It may be required for diabetes patients and subjects at risk fordiabetes to measure their blood glucose levels regularly in an attemptto keep their blood glucose levels within an acceptable range, and tomake an accurate recordation of blood-glucose levels for both personaland medical records. In one aspect of the present invention, theinstrument may also comprise an alphanumeric display for displaying themeasured blood-glucose concentration. The alphanumeric display of thisembodiment may comprise a visual display and an audio display. Thevisual display may be a liquid crystal display (LCD), a plasma displaypanel (PDP), and a field emission display (FED) or any other functionalequivalent known in the art. An audio display, capable of transmittingalphanumeric data and converting this alphanumeric data to an audiodisplay, may be provided with an audio source comprising recorded audioclips, speech synthesizers and voice emulation algorithms or any otherfunctional equivalent known in the art.

Self-Monitoring of Blood Glucose (SMBG) is an ongoing process repeatedmultiple times per day for the rest of the diabetic patient's lifetime.Accurate recordation of these measurements are crucial for diagnosticpurposes. A facile storage and access system for this data is alsocontemplated in this invention. In one aspect of the present invention,an instrument for non-invasively measuring blood-glucose concentrationfurther comprises a microprocessor and a memory which is operativelylinked to the microprocessor for storing the blood glucose measurements.The instrument of this embodiment further comprises a communicationsinterface adapted to transmit data from the instrument to a computersystem. In this embodiment the communications interface selected mayinclude, for example, serial, parallel, universal serial bus (USB),FireWire, Ethernet, fiber optic, co-axial, and twisted pair cables orany other functional equivalent known in the art.

In addition to storing blood-glucose measurement data within aninstrument, the present invention includes a computer system fordownloading and storing these measurement data to facilitate storage andaccess to this information. The present invention further contemplates acomputer processor, a memory which is operatively linked to the computerprocessor, a communications interface adapted to receive and send datawithin the computer processor, and a computer program stored in thememory which executes in the computer processor. The computer program ofthis embodiment further comprises a database, wherein data received bythe database may be sorted into predetermined fields, and the databasemay be capable of graphical representations of the downloaded analyteconcentrations. The graphical representations of this embodiment mayinclude, but are not limited to, column, line, bar, pie, XY scatter,area, radar, and surface representations.

The computer system contemplated by the present invention should beaccessible to a remote access user via an analogous communicationsinterface for use as a diagnostic, research, or other medically relatedtool. Physicians, for example, could logon to the computer system viatheir analogous communications interface and upload a patient'sblood-glucose measurements over any period of time. This informationcould provide a physician with an accurate record to use as a patientmonitoring or diagnostic tool such as, for example, adjusting medicationlevels or recommending dietary changes. Other remote access userscontemplated may include research institutes, clinical trial centers,specialists, nurses, hospice service providers, insurance carriers, andany other health care provider.

The present invention has demonstrated that glucose may benon-invasively measured using a mid-infrared signal from a body surface.Studies may be performed in a variety of systems, including studies withhuman corneas, in vitro studies using glucose solutions on membranesamples, rabbit studies with varying blood glucose concentrations, andhuman studies with diabetic or non-diabetic human volunteers.

The human studies will demonstrate a dose-response to glucoseconcentration.

EXAMPLES

The following examples are provided to describe and illustrate thepresent invention. As such, they should not be construed to limit thescope of the invention. Those in the art will well appreciate that manyother embodiments also fall within the scope of the invention, as it isdescribed hereinabove and in the claims.

Example 1

Experimental In-Vitro Model to Test Precision and Accuracy of theInstrument

Instrumentation

An instrument used for the Mid-infrared measurements may be the SOC 400portable FTIR. The SOC 400 portable FTIR is based on an interferometerand was originally designed for the US Army to detect battlefield gases.This instrument may be modified to allow measurements on rabbit andhuman eyes. These modifications may include the installation of a filterto allow only energy in a desired wavelength region, such as between 7to 13 micron region, to be measured, and also the modification of thefaceplate to permit easier placement of the instrument for rabbit andhuman studies.

In Vitro Studies

Studies are performed to demonstrate that solutions with varyingconcentrations of glucose would give a Mid-infrared dose-response.Hydrophilic polyethylene membranes from Millipore Corporation aresaturated with glucose solutions with concentrations at 2000 mg/dL andlower. The samples are warmed to approximately body temperature beforemeasurements are taken, which simulates the natural mid-infraredradiation from a subject's body.

Example 2

Experimental Rabbit Model

An initial test is conducted using two adult rabbits having glucosevalues below 150 mg/dL. The rabbits are anesthetized with an IMinjection of ketamine/xylazine/acepromazine according to the protocoldescribed in Cameron, et al., 1(2) DIABETES TECH. THER., 135–143 (1999).The rabbit is immobilized such that after anesthesia the eyeball isavailable for measurements with the non-invasive glucose monitor ascontemplated in the present invention.

Once the animals are unconscious, a drop of blood from the ear vein ofeach is taken and tested on a blood glucose test strip with a bloodglucose meter. Such samples are taken every fifteen minutes throughoutthe study.

Each rabbit is placed in front of, or under, a non-invasive glucosemonitor as contemplated in the present invention, or such instrument isbrought up to a body surface of the rabbit, and a series of measurementsare taken over the next several hours. One rabbit is tested by simplymeasuring the infrared radiation naturally emitted from the rabbit'seye. The second rabbit will be tested by flooding infrared radiationonto the rabbit's eye and measuring the reflected signal. Every fifteenminutes a blood glucose test is performed using a drop of blood fromeach rabbit for comparison with the data generated using thenon-invasive glucose monitor of the present invention. The datagenerated in this study is used to show that the instrument according tothe present invention is measuring blood glucose concentration.

Ketamine Anesthetized Rabbit Studies

As noted in the scientific literature (Cameron et al., DIABETES TECH.THER., (1999) 1(2):135–143), rabbits anesthetized with Ketamineexperience a rapid and marked increase in blood glucose concentration,due to the release of glucose from the liver. Rabbit blood sugar canchange from ˜125 mg/dL to ˜325 mg/dL in 60 minutes, as measured with aLXN ExpressView blood glucose meter. These experiments require apreliminary use of gas anesthesia (Isoflorane) prior to the use ofKetamine. The gas must be discontinued in order for the Ketamine effectto manifest itself. The drying out of the eye may be prevented bysuturing the eyelids and using the sutures to open the eye for themeasurement and then allowing them to close after the measurement tomoisten the eyeball. Once the rabbit is treated with the ketamine,measurements are taken from the eye of the rabbit to measure its naturalmid-infrared radiation and glucose concentration.

Example 3

Human Clinical Study

Human Studies

Several studies may be performed with non-diabetic and diabetic humanvolunteers. Several experiments with a diabetic volunteer may beperformed. The subject is asked to adjust his food intake and insulinadministration in order to have his glucose levels move fromapproximately 100 to 300 mg/dL over a three to four hour timeframe.During the study, the patient takes duplicate fingerstick glucosemeasurements every ten to fifteen minutes and is scanned with the SOC400 approximately every fifteen minutes. Prior to collecting theinfrared scan, the instrument operator aligns the SOC 400 with thesubjects' eye to attempt to collect the strongest signal. Measurementsof the mid-infrared radiation emitted from the subject's eye are takenand glucose concentration is measured.

Example 4

A Method Wherein a Remote Access User Can Receive a Subject's MeasuredAnalyte Concentrations Which Have Been Downloaded and Stored in aComputer System

One aspect of the present invention relates to a method of downloadingand storing a subject's measured analyte concentrations (FIG. 4). Asubject first measures the analyte concentration from a body surfacesuch as their eye (100), whereby naturally emitted mid-infraredradiation (150) is measured using a non-invasive instrument (200). Thenon-invasive instrument (200) further comprises a communicationsinterface (250) which is capable of connecting (300) the non-invasiveinstrument (200) through the communications interface (250) to acomputer system (400). The communications interface (250) isspecifically adapted to transmit data from the instrument to thecomputer system (400). The computer system (400) comprises a computerprocessor, a computer program which executes in the computer processor,and an analogous communications interface (450). The measured analyteconcentrations from the non-invasive instrument (200) are downloaded viathe communications interface (250) to the computer system (400). Aremote access user (500), having a computer system with an analogouscommunications interface (450) is capable of retrieving the downloadedmeasured analyte concentrations from the computer system (400). Thecommunications interfaces (250, 450) may include, for example, serial,parallel, universal serial bus (USB), FireWire, Ethernet, fiber optic,co-axial, and twisted pair cables. This information is used, forexample, to provide data, warnings, advice or assistance to the patientor physician, and to track a patient's progress throughout the course ofthe disease.

1. A method of determining an analyte concentration in a tissue of asubject, the subject including an eye with an occular surface and aconjunctiva surface, comprising the steps: a. detecting naturallyoccurring mid-infrared radiation emitted from the conjunctiva withoutcontact with the ocular surface using a non-invasive instrumentcomprising a mid-infrared detector; b. comparing a radiation signatureof said mid-infrared radiation to a radiation signature of mid-infraredradiation corresponding to an analyte concentration; and c. analyzingsaid radiation signature of said mid-infrared radiation from saidsubject to determine said analyte concentration in a tissue of saidsubject.
 2. The method of claim 1, wherein said analyte is selected fromthe group consisting of metabolic compounds or substances,carbohydrates, sugars, glucose, proteins, peptides, amino acids, fats,fatty acids, triglycerides, polysaccharides, alcohols, ethanol, toxins,hormones, vitamins, bacteria-related substances, fungus-relatedsubstances, parasite-related substances, pharmaceutical compounds,non-pharmaceutical compounds, pro-drugs, drugs, and any precursor,metabolite, degradation product or surrogate marker.
 3. The method ofclaim 2, wherein said analyte is glucose.
 4. The method of claim 1,wherein said naturally occurring mid-infrared radiation comprisesinfrared radiation having wavelengths between about 2.5 microns andabout 25.0 microns.
 5. The method of claim 1, wherein said detectingstep further comprises selecting and detecting desired wavelengths ofsaid naturally occurring mid-infrared radiation.
 6. The method of claim1, wherein said comparing step and said analyzing step further compriseusing a microprocessor.
 7. A method of downloading and storing asubject's measured analyte concentration, comprising the steps of: a.measuring said analyte concentration according to the method of claim 1,using a non-invasive mid-infrared detecting instrument having acommunications interface; b. connecting said instrument through saidcommunications interface to a computer system having a computerprocessor, a computer program which executes in said computer processor,and an analogous communications interface; and c. downloading from saidinstrument to said computer system said measured analyte concentrations.